The present invention relates to a rotating electric machine in which a cooler for cooling a coolant is provided, as well as to a method of cooling a rotating electric vehicle.
A rotating electric machine in which a cooler for cooling a coolant is provided has been described, for example, in Japanese Patent Laid-open Nos. Hei 7-177705 and Hei 10-146022. The rotating electric machine described in these documents is configured such that a space between a stator frame and a stator iron core is partitioned into a low temperature gas chamber, to which a coolant at a low temperature is supplied, and a high temperature gas chamber, in which the heated coolant flows. A plurality of coolers distributed in the axial direction are provided in a foundation pit under the rotating electric machine, whereby the coolant cooled by the plurality of coolers and boosted by a ventilating fan is introduced to various heat sources, such as the iron core and the coils, via the low temperature gas chamber, and the coolant which has been used for cooling the heat sources is returned to the coolers via the high temperature gas chamber. 
The above-described rotating electric machine, however, has a problem. Since the coolant which has passed through one or two or more of the heat sources is then introduced to a central portion of the iron core, the temperature of the coolant is raised before the coolant reaches the central portion of the iron core. Accordingly, for the above-described rotating electric machine, if a thermal load generated from the heat sources, such as the iron core and coils, becomes large with an increase in the generation capacity or in the loss density, the cooling effect of the coolant introduced to the central portion of the iron core is significantly degraded. As a result, in the above-described rotating electric machine, there is a possibility that local heat generation will occur in a gap between the stator iron core and a rotor iron core, thereby to increase the thermal oscillation stroke of the rotor due to uneven thermal expansion of the rotor in the axial direction.
To solve the above-described problem, there may be considered a method of increasing the amount of the coolant or optimizing the distribution of the amounts of the coolant components supplied to respective ventilating passages by adjusting the ventilating resistance; however, according to the former method, the ventilation loss of the coolant caused upon boosting the coolant by the fan becomes larger, to increase the total loss in the coolant; and, according to the latter method, since the ventilation resistance must be adjusted while the desired electric and mechanical characteristics are satisfied in a limited space, it is difficult to optimize the distribution of the coolant components supplied to the respective ventilating passages.
An object of the present invention is to provide a rotating electric machine which is capable of exhibiting a level axial temperature rise distribution, and a cooling method thereof.
The basic feature of the present invention is to supply a coolant, which is sufficiently cooled, to a central portion of an iron core which is most distant from both axial ends of the iron core. To realize this feature of the present invention, a plurality of ventilating passages, which continuously extend in the peripheral direction, are provided in the axial direction between a stator frame and a stator iron core, and coolers are provided in at least those passages, which communicate with the central portion of the iron core, of the plurality of ventilating passages formed in the axial direction, wherein the coolant boosted by a booster is cooled by the coolers and is allowed to flow to the central portion of the iron core in the direction from the outer peripheral side to the inner peripheral side of the iron core via the ventilating passages.
If an even number of ventilating passages are provided, two to four of the ventilating passages, which are located on the central side, constitute the ventilating passages which communicate with the central portion of the iron core. If an odd number of ventilating passages are provided, one to three of the ventilating passages, which are located on the central side, constitute the ventilating passages which communicate with the central portion of the iron core. The number of the ventilating passages is dependent on the capacity of the rotating electric machine. For example, for a generator having a generation capacity of 100 MW class, at least three ventilating passages are provided, and for a generator having a generation capacity of 350 MW class or more, seven to ten or more ventilating passages are provided.
According to the above feature of the present invention, it is possible to level the axial temperature rise distribution in the machine. In particular, the above feature is effective in a rotating electric machine in which the axial length is long and air is used as a coolant, for example, an air-cooled generator having a large capacity. Air which is larger in viscosity than hydrogen exhibits a high ventilating resistance when it flows in a generator, to thereby cause a temperature rise. The longer the ventilating distance of air, the larger the ventilating resistance will be. As a result, for a generator which is longer in axial length and larger in capacity, the temperature rise of the air becomes significantly larger, and the amount of the air supplied to the central portion of an iron core becomes smaller.
Accordingly, a small amount of air whose temperature is raised is supplied to the central portion of the iron core which is most distant from both the axial ends of the iron core, with a result that there occurs a difference in temperature between each of the axial ends of the iron core and the central portion of the iron core. According to the present invention, it is possible to supply a coolant which is sufficiently cooled to the central portion of the iron core, however, it is also possible to suppress the temperature rise of the central portion of the iron core to an allowable value or less, and, hence, to level the axial temperature rise distribution in the machine.
The leveling of the axial temperature rise distribution in the machine means that the temperature rise of the central portion of the iron core is suppressed to an allowable value or less, to reduce the difference in temperature between each of the axial ends of the iron core and the central portion of the iron core. Accordingly, there is no variation in the axial temperature rise distribution in the machine.